Engine Coolant Temperature (ECT)

The Engine Coolant Temperature (ECT) sensor is a component found in the vehicle's engine. Below, you will learn exactly what it is, how it works, and its usefulness. As well as, where it is located and what are the failures it commonly presents.

What is the Engine Coolant Temperature Sensor?

The ECT sensor is a very important device in the engine. It uses a resistor, which induces a voltage drop to the machine so that the air/fuel composition is set and the injector pulse is stabilized. In this way, the temperature can be calculated.

Likewise, the coolant temperature sensor is in charge of sending information to the vehicle's computer to activate the ventilation mode.

This is responsible for measuring the temperature and monitoring the cold start, this is because the injection systems have begun to maneuver. Therefore, a sensor is needed to alert and send information to the ECU to vary the amount of fuel as needed.

What is the Engine Coolant Temperature Sensor used for?


The primary function of the ECT sensor is to calculate the temperature of the engine coolant. It then sends this information to the computer, which is in charge of controlling and normalizing the injection system, as well as modifying the air/fuel composition.

How does the ECT sensor work?

Because it is a thermistor, the hotter it gets, the lower the resistance is. Therefore, it sends a signal to the ECU, which is not linear, but proportional. Thanks to this, the ECU can receive the information, decipher the values and transform them into a coolant temperature index.

On the other hand, if the engine is cold, the machine increases the fuel injection time, as well as the ignition persistence. However, the engine temperature is taken into consideration, so that it does not drop so low that it shuts down. In this case, the Check Engine Light on the dashboard will come on.

ECT Sensor Types

The only type of ECT sensor that exists is the NTC thermistor, which means a negative temperature factor resistor. So, when the temperature is very high, the conductivity of the sensor is higher. However, this relationship is not linear, but adjustable. That is, it does not perform Ohm's law.

Common ECT Sensor Failures

The coolant temperature sensor is a fundamental part of the engine because if it does not perform its function well, it will also affect the injection system. So, you must recognize what are some of the most common failures. Among them we can mention:

  • When trying to start the car when it is cold, problems occur.
  • Idling or hesitant idling.
  • Even if the engine temperature is optimal, difficulties arise when starting.
  • Excessive fuel consumption.
  • Inconveniences when activating the electric cooling fans.

OBD2 codes concerning the Coolant Temperature Sensor

The ECT sensor is responsible for sending information to the computer and the injector system. In this way, the engine operates normally. However, when faults occur, they must be differentiated from each other in order to attack the problem. Thus, OBD2 codes have been established, among which are:

P0117: Generated when there is low voltage.

P0118: Response to high voltage.

P0070: There is a fault in the sensor circuit.

How to test if the Coolant Temperature Sensor is working?

It is necessary to know how to test the ECT sensor in order to diagnose any fault. In this case, you must check if the ECU is outside the minimum and maximum temperature measurements. If so, there is a fault in the NTC resistor of that sensor, so it has an opening in the circuit.

In addition, it will present all the above-mentioned faults. Therefore, to verify that it is in perfect function, it must show the following values:

Between points C and A, the resistance should be 2.5 kΩ when the coolant temperature is at 20º Celsius. This is used as an intervention signal in the injection method.

On the other hand, when the coolant temperature is at 80º Celsius, the resistance should be about 0.05 kΩ, between points C and A. In this case, it serves as an indication of instrumentation in the tool compartment.

How to clean the ECT sensor?

If you want to clean the ECT sensor, you only need to know where it is located. Once it is displayed, it is unscrewed for maintenance from the outside. Now that you have it in your hands, you must wash it well.

To do this, use a spray to spray it well. Also, finish the process by drying it with pressurized air. This is important because the old liquid accumulated in the coolant can cause the sensor to fail.

Engine Coolant Temperature Sensor Location

To find the location of the ECT sensor you must go to the depth or bottom of the engine. There, you will find it threaded either in the internal intake compound or in the cylinder head. It will always be close to the coolant passage area to have continuous contact with the fluid. You can find out the exact location of the ECT sensor by acquiring the car's electrical diagrams.


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